Fix has_constant_parameter_count() confusion in LReturn

src/x87/lithium-codegen-x87.cc

Index: src/x87/lithium-codegen-x87.cc
diff --git a/src/x87/lithium-codegen-x87.cc b/src/x87/lithium-codegen-x87.cc
index 284a66640422db8b884f2331e076c0f3e2e4ced8..2b6c26596994e8b943d5ea4dc65b846601f69ffa 100644
--- a/src/x87/lithium-codegen-x87.cc
+++ b/src/x87/lithium-codegen-x87.cc
@@ -3050,6 +3050,7 @@ void LCodeGen::EmitReturn(LReturn* instr, bool dynamic_frame_alignment) {
     }
     __ Ret((parameter_count + extra_value_count) * kPointerSize, ecx);
   } else {
+    DCHECK(info()->IsStub());  // Functions would need to drop one more value.
     Register reg = ToRegister(instr->parameter_count());
     // The argument count parameter is a smi
     __ SmiUntag(reg);